Where VFD should be placed?

Wednesday, December 17, 2014

Most of the users installed variable frequency drive (VFD) near the MCC because it's easy to maintain the system but there are some issue's which may happen due to placing the VFD near the MCC like there is a kind voltage reflection issue if the length of the cable is more than the critical length which may damage the motor.

In this case we need to follow instructions given in the user's manual supplied with the variable frequency drive. Generally following are recommended by manufacture:

Variable frequency drives have electrical, electronic and power semiconductor devices or modules such as (IGBTs, Thyristors, Diodes etc.) These devices are temperature sensitive and are not rugged compare to Contactors, Breakers and Overloads installed inside panels or mcc resulting the chances of failure of components inside VFD is more at higher ambient temperature compare to others. If VFD does not get sufficient air flow and subject to ambient temperature higher then recommended by manufacturer then VFD is derated and would be able to give less current then its rated or sized for and may be damaged and its warranty may be void by supplier.

Regarding cables, check in manual insulation rating of cable. Typically it is 75 C and if we size the cable on the basis of 90 C insulation, this may become additional source of heat for VFD and the motor. Sizing cable properly as per relevant code (NEC, CEC or whichever applicable) so that voltage may not drop more than recommended by the code. Control and Signal cable should be separated from power cable to avoid noise in signal. Check user/Installation manual or contact variable frequency drive suppliers/manufacturers.